Do reviewers become biased about research papers written by authors of a previous low quality paper?

I would distinguish between two papers in parallel (as in your example) versus a history of bad papers.

If I'm seeing a good paper and a bad paper that share an author, and I don't yet know that author well, then the bad paper probably won't affect my opinion of the good paper too badly (unless we are talking really embarrassingly bad). I'll have a mixed opinion, but I'm still forming it.

On the other hand, there are certainly some authors who have built up a history with me such that I see their paper and think: "Oh no, I hope they've learned from last time."

In psychology, there is the phenomenon of "anchoring" - a first impression colours the rest of a transaction, whether it is negotiating a price, opinion about personality or other issues.

This indicates that, yes, a bad first paper which captures the attention of the reviewer can have a detrimental effect on how subsequent work is seen. If it is a novel researcher, the memory of the name may not be retained, so, the effect might be milder, but if there are two papers in one conference from the same author, and reviewed by the same people, that effect may indeed hold.

This is a reason why many conferences espouse double-blind reviews (although I am not a friend of this for other reasons which are outside the scope of this question).